A pushbutton structure has been a primary component on home appliances, testing meters and computer peripherals, and all of these products can be easily controlled through designs of pushbuttons.
A membrane printed circuit board inside the pushbutton structure utilized by a common computer or notebook computer primarily comprises an upper layer membrane, a lower layer membrane and an insulation layer arranged by stacking. Besides, there is no glue applied on any of the three layers so that when a rubber body is pressed down to squeeze air, the contact point of the upper layer membrane and that of the lower layer membrane will touch each other. In an event that a water drop has dripped into the inside of a keyboard by a user, there will not be a short-circuit problem generated on the membrane printed circuit board at first. However, as soon as the rubber body begins to restore from a pressed-down manner, it will absorb the water drop from inside the keyboard to the membrane printed circuit board due to the vacuum force generated by the rubber body, which will result in short-circuit problem on the membrane printed circuit board.
On the other hand, there is another kind of printed circuit board primarily comprising an upper layer membrane and lower layer membrane made of soft plastic. A plurality of conductive portions are printed on the upper layer membrane, whereas a plurality of contact portions corresponding to the conductive portions are printed on the lower layer membrane; also, an insulation portion is printed on each of the contact portions, and then the insulation portion, the upper layer membrane and the lower layer membrane are glued together to form a membrane printed circuit board.
Moreover, some people in the industry have developed several kinds of waterproof keyboard structures with different designs to improve the waterproof structure of a keyboard, which are listed below:
1. A membrane that is provided on the lower side of a circuit unit in a waterproof keyboard is disclosed at Taiwan Patent Gazette Publication No. 470190 entitled “Waterproof Keyboard”, wherein the membrane is closely connected to a resilient rubber body of the keyboard so that the circuit unit can be sealed between the resilient rubber body and the membrane.
2. A structure of waterproof keyboard is disclosed at Taiwan Patent Gazette Publication No. 476429 entitled “Waterproof Keyboard”. The waterproof keyboard includes: a top lid and a base, wherein a plurality of pushbuttons are provided encased on the surface of the top lid; a positioning structure protruding downwards and extending from the bottom face of the top lid to the base to be connected to the base so that the top lid can be fastened to the base; a conducting sheet located on the upper side of the base; and a resilient body located on the upper side of the conducting sheet, wherein a positioning hole on the resilient body is provided so that the positioning structure can pass through the positioning hole, and the perimeter of the positioning structure is designed to be closely fitted into the positioning hole on the resilient body so that the moisture permeating in from the top lid can be blocked on the resilient body.
3. A structure of waterproof keyboard is disclosed at Taiwan Patent Gazette Publication No. 504026 entitled “Waterproof Keyboard”, wherein a groove is provided on the top lid of the keyboard, and a plurality of drainage holes are provided at the front edge of the groove for passing through therein to the bottom of the top lid and are downwardly connected to a plurality of drainage columns. Also, a plurality of fitting-in columns corresponding to the drainage columns are provided on the base of the keyboard, and a through-hole is formed inside of each fitting-in column so that a drainage can insert into its corresponding through-hole of the fitting-in column.
Aside from the above-mentioned, there are more waterproof keyboard structures that are similar to the foregoing keyboard structures, including Taiwan Patent Gazette Publication No. 477446 entitled “Waterproof Keyboard”, Taiwan Patent Gazette Publication No. 464012 entitled “Structure of Waterproof Keyboard for Notebook Computer”, Taiwan Patent Gazette Publication No. 385891 entitled “Waterproof Keyboard”, Taiwan Patent Gazette Publication No. 369191 entitled “Waterproof Keyboard”, Taiwan Patent Gazette Publication No. 358571 entitled “Waterproof Keyboard”, Taiwan Patent Gazette Publication No. 342983 entitled “Structure of Waterproof Keyboard”, and Taiwan Patent Gazette Publication No. 236428 entitled “Improved Structure of Waterproof Keyboard”.
Despite that the waterproof effect can be achieved by the foregoing improved designs for the membrane printed circuit board or by combining an improved keyboard structure to a conventional membrane printed circuit board, the process flow for redesigning a printed circuit board is still very complicated. Therefore, it is time consuming and labor consuming to do the redesigning. Moreover, it is difficult to make a precise positioning for the relative components; therefore, the production cost will also become higher.